Calling i2c set speed twice for i2c_mux_bus

[Michal Simek]

Hi Heiko,

On 10. 04. 20 7:11, Heiko Schocher wrote:
> Hello Michal,
> 
> Am 09.04.2020 um 16:03 schrieb Michal Simek:
>> Hi Heiko and Simon,
>>
>> I have find out one bug in i2c class. I am using zcu104 revC board which
>> has dts in mainline where i2c1 has i2c mux with some channels.
>> In DT clock-frequency = <400000>; is specified and it is read in
>> i2c_post_probe(). But i2c_mux_bus_drv is also UCLASS_I2C which means
>> that post probe is called for it too. And because clock-frequency
>> property is not there default 100k is used.
>>
>> I think that is bug and should be fixed.
>> Heiko: Are you aware about this issue?
> 
> No :-(
> 
> The question is, is this a bug?

I have never seen clock-frequency property in i2c mux bus node. Also I
have looked at linux dt binding docs and nothing like that is specified
there. From quick look also pca954x driver is not reading it.

> Should a i2c bus behind a mux not be able to set his own speed?

Not sure if that make sense but Linux will likely ignore it. I am not
saying it doesn't make sense but I haven't seen this feature.


> But may as a feature (or bugfix?) if "clock-frequency" is not there,
> use the speed of the parent bus...?

I was thinking about this too.
just c&p quick implementation would look like this. Because it is
i2c->i2c_mux->i2c. But maybe there is a better way how to do it.

diff --git a/drivers/i2c/i2c-uclass.c b/drivers/i2c/i2c-uclass.c
index 2aa3efe8aaa0..982c467deba3 100644
--- a/drivers/i2c/i2c-uclass.c
+++ b/drivers/i2c/i2c-uclass.c
@@ -640,9 +640,21 @@ static int i2c_post_probe(struct udevice *dev)
 {
 #if CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)
        struct dm_i2c_bus *i2c = dev_get_uclass_priv(dev);
+       int parent_speed = I2C_SPEED_STANDARD_RATE;
+
+       if (dev->parent &&
+           device_get_uclass_id(dev->parent) == UCLASS_I2C_MUX &&
+           dev->parent->parent &&
+           device_get_uclass_id(dev->parent->parent) == UCLASS_I2C) {
+               struct dm_i2c_bus *i2c_parent;
+
+               i2c_parent = dev_get_uclass_priv(dev->parent->parent);
+               parent_speed = i2c_parent->speed_hz;
+               /* Not sure if make sense to check that parent_speed is
not 0 */
+       }

        i2c->speed_hz = dev_read_u32_default(dev, "clock-frequency",
-                                            I2C_SPEED_STANDARD_RATE);
+                                            parent_speed);

        return dm_i2c_set_bus_speed(dev, i2c->speed_hz);
 #else

Thanks,
Michal